1. Field of the Invention
The present invention relates generally to a method of fabricating circuit traces on a plastic substrate. More particularly, the present invention relates to a method of making a molded interconnect device.
2. Description of the Prior Art
As known in the art, molded interconnect devices (MIDs) have been used in many applications such as automotive and telecommunication industries. MIDs essentially integrate mechanical and electrical functions into one piece and make an important contribution to design in terms of manufacturability and assembly. Unlike printed circuit boards, which are typically limited to two-dimensional planes, MIDs can implement three-dimensional circuitry. Among other things, a circuit pattern with multiple planes allows better spacing of circuitry, as well as the connected switches and buttons.
Many approaches have been developed for making an MID up to the present. The methods for fabricating an MID and their respective shortcomings can be summarized as follows.
(1) Laser direct structuring (LDS) technique. This method involves the use of a plastic material impregnated with metal catalyst. The plastic material is activated by laser method. After this, the plastic material is metallized using chemical copper process. U.S. publication No. 2007/0247822 discloses such method. The shortcomings of this method include high production cost due to expensive metal catalyst impregnated plastics and laser tools, and environmental pollution issues due to wet chemical process.
(2) Microscopic integrated processing technology (MIPTEC). This prior art method uses chemical vapor deposition (CVD) or sputtering to coat plastic material with conductive material, then uses laser to pattern the conductive material and remove the conductive material from the non-metallized area, followed by chemical copper metallization. The shortcomings of this method include high production cost due to expensive CVD or sputtering tool as well as environmental pollution issues due to wet chemical process.
(3) Hot embossing method. This prior art method is a technique of imprinting microstructures on a substrate (polymer) using a master mold. One of the drawbacks is that the cost of developing molds is high. Besides, there are difficulties of three-dimensional processing.
(4) Two-shot molding method. This method involves two different plastic materials formed by respective injection mold steps. The two different plastic materials include activable and non-activable plastics. The activable plastic is then metallized by wet chemical processes. The drawbacks include bottleneck of mold development, low design flexibility and high cost of development.
In light of the above, there is a need in this industry to provide an improved method of fabricating MIDs, which is cost-effective (no laser tool, CVD tool or sputtering tool is required), flexible and has no environmental pollution issues, thereby overcoming the prior art problems and shortcomings.